In many generating systems, particularly those that operate at high speeds, it is highly desirable to eliminate brushes since they frequently require maintenance or replacement and are perhaps the single weakest point in the system in terms of breakdowns and the like. Moreover, by their very nature, they may introduce transients into the electrical energy being outputed which in turn may interfere with the proper operation of some types of electrical loads being driven thereby.
A typical brushless generator has three distinct generating systems, including a main generator, an exciter and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is employed to induce current in a set of windings. This induced current is in turn employed to generate a magnetic field in the exciter; and this magnetic field in turn is employed to induce an even higher level of current, typically three phase alternating, which is then employed to generate a magnetic field for the main generator.
In order to avoid the use of brushes, it is necessary that the magnetic field in the main generator be in the rotor so that the output of the system can be taken from the stator of the main generator. And in order to generate a suitable magnetic field in the rotor, it is necessary to utilize direct current, as opposed to alternating current, for the same. Since the output of the exciter is an alternating current, this current must be rectified to direct current. And again, in order to avoid resort to brushes, it is accordingly necessary that the rectifier interconnecting the exciter and the main generator field winding be carried by the rotor of the generator. U.S. Pat. No. 3,577,002 issued May 4, 1971 to Hall et al is generally illustrative of this approach although it does show a commutator and brush structure which is necessary for alternative use of the generating system as a starter motor.
Because the rectifier assembly is carried by the rotating shaft of the generating system, it is subjected to high centrifugal loading and much care must be taken to assure that the components of the rectifier are adequately supported against such forces. It will also be appreciated that it is highly desirable to minimize the space occupied by the rectifier assembly since it typically is housed within the shaft itself. Finally, it is desirable to make provision for cooling the rectifier assembly during operation since such not only minimizes the possibility of thermal damage to the components, but provides a greater capacity over a correspondingly sized, uncooled rectifier assembly.
It is also desirable that the assembly be such that it may be easily removed for servicing in the event of component failure.
The present invention is directed to the provision of a semiconductor assembly, typically a rectifier assembly, having the foregoing attributes.
Prior art of possible relevance includes the following U.S. Pat.: Nos. 3,400,307 issued Sept. 3, 1968 to Baker et al; 3,800,191 issued Mar. 26, 1974 to Newton; and 4,338,652 issued July 6, 1982 to Romanczuk et al.